AU756930B2 - Method and system for locating a mobile subscriber in a CDMA communication system - Google Patents
Method and system for locating a mobile subscriber in a CDMA communication system Download PDFInfo
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- AU756930B2 AU756930B2 AU58069/99A AU5806999A AU756930B2 AU 756930 B2 AU756930 B2 AU 756930B2 AU 58069/99 A AU58069/99 A AU 58069/99A AU 5806999 A AU5806999 A AU 5806999A AU 756930 B2 AU756930 B2 AU 756930B2
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- H—ELECTRICITY
- H04—ELECTRIC COMMUNICATION TECHNIQUE
- H04W—WIRELESS COMMUNICATION NETWORKS
- H04W64/00—Locating users or terminals or network equipment for network management purposes, e.g. mobility management
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/0205—Details
- G01S5/0218—Multipath in signal reception
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S5/00—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations
- G01S5/02—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves
- G01S5/12—Position-fixing by co-ordinating two or more direction or position line determinations; Position-fixing by co-ordinating two or more distance determinations using radio waves by co-ordinating position lines of different shape, e.g. hyperbolic, circular, elliptical or radial
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- Computer Networks & Wireless Communication (AREA)
- Signal Processing (AREA)
- Mobile Radio Communication Systems (AREA)
- Position Fixing By Use Of Radio Waves (AREA)
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Abstract
The present inventation provides a base station comprising:
a plurality of antennas, each of the antennas separated by a known distance;
means for transmitting a first spread spectrum signal having a first code;
means for receiving, using the plurality of antennas, a second spread spectrum signal having a second code, the second spread spectrum signal time synchronized with the first spread spectrum signal;
means for making a distance determination based on in part a timing difference between the second code of the received second spread spectrum signal and the first code of the base station's transmitted first spread spectrum signal;
means for comparing a phase difference of a carrier signal of the second spread spectrum signal as received by each of the plurality of antennas; and
means for determining an angle of the received second spread spectrum signal using the known distance between the antennas and the phase difference; and
means for determining a location of a source of the second spread spectrum signal using the determined angle and the distance determination.
Description
WO 00/57661 PCT/US99/20257 METHOD AND SYSTEM FOR LOCATING A MOBILE SUBSCRIBER IN A CDMA COMMUNICATION SYSTEM Field of the Invention This invention generally relates to spread spectrum code division multiple access (CDMA) communication systems. More particularly, the present invention relates to a system and method that determines the geographic location of a subscriber unit within a CDMA communication system.
Description of the Prior Art Wireless systems capable of locating a subscriber are presently known in the art. One wireless technique uses the global positioning system (GPS). In GPS, the communication handset receives data transmitted continuously from the 24 NAVSTAR satellites. Each satellite transmits data indicating the satellite's identity, the location of the satellite and the time the message was sent. The handset compares the time each signal was received with the time it was sent to determine the distance to each satellite. Using the determined distances between the satellites and the handset along with the location of each satellite, the handset can triangulate its location and provide the information to a communication base station. However, the incorporation of a GPS within a subscriber unit increases its cost.
.19-04-2001 uN, r. C. US 009920257 Another subscriber location technique is disclosed in U.S. Patent No.
5,732,354. A mobile telephone using time division multiple access (TDMA) as the air interface is located within a plurality of base stations. The mobile telephone measures the received signal strength from each of the base stations and transmits each strength to each respective base station. At a mobile switching center, the received signal strengths from the base stations are compared and processed. The result yields the distance between the mobile telephone and each base station. From these distances, the location of the mobile telephone is calculated.
Wireless communication systems using spread spectrum modulation techniques are increasing in popularity. In code division multiple access (CDMA) systems, data is transmitted using a wide bandwidth (spread spectrum) by modulating the data with a pseudo random chip code sequence. The advantage gained is that CDMA systems are more resistant to signal distortion and interfering frequencies in the transmission path than communication systems using the more common time division multiple access (TDMA) or frequency division multiple access (FDMA) techniques.
EP 0 865 223 A2 is a position estimation scheme for a cellular mobile system. A first and a second signal sequence are exchanged between the mobile station and the base station. These signals may be CDMA signals. A phase difference between the first and second sequence is used to determine a distance P-2ingszeit 19.Apr, 15:48 AMENDED
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n vv v vUULrt. AINU KUENIG.P.C.
.19-04-2001 US 009920257 between the mobile and base station. Using multiple base stations, the position is estimated using triangulation.
U.S. Patent No. 5,600,706 is a position systemusing a range determination in a CDMA system. The system uses pilot signals and time difference of arrival (TDOA) and absolute time of arrival (TOA) in the position determination.
WO 98/18018 discloses locating a mobile terminal using two antennas of an array in a time division multiple access communication system. A phase difference in the signals received by the two antennas is used to determine an angle from the centerline of the antennas to the mobile terminal. Received signal strength is used to estimate the terminal's distance. The terminal's location is determined using the determined angle and distance.
WO 97/47148 discloses determining aposition of amobile terminalwithin a cellular system. A signal is transmitted at a low power level. The power level is temporarily increased. The signal transmitted at the increased power level is used to make a position measurement of the terminal.
U.S. Patent No. 5,736,964 discloses a CDMA system for locating a communication unit. A base station transmits a location request to the unit. The unit transmits a receive time of the message to the base station. A group of base stations also determine a receive time of a symbol sequence in the unit's transmissions. Using the time measurements, the location of the unit is determined.
_-2a- Pfansszeit 19.Apr. 15:48 AMENDEDSHEET .19-04-2001 :48 FAX 215 568 6499 VOLPE AND KOENIG,P.C. US 009920257 U.S. Patent No. 5,506,864 discloses a system for determining a distance between a base station and a remote unit in a CDMA system. The base station transmits a base CDMA signal to the remote unit. The remote unit transmits a remote CDMA signal to the base station. The remote CDMA signal has its timing synchronized to the received base CDMA signal. The base station determines the distance to the remote unit by comparing the chip code sequences of the transmitted base CDMA signal and the received remote CDMA signal.
There exists a need for an accurate mobile subscriber unit location system that uses data already available in an existing CDMA communication system.
-2beit 19.Apr. 15:48 AMENDED SHEET 3 SUMMARY OF THE INVENTION A subscriber unit is geographically located using a plurality of base stations in a wireless CDMA communication system. Each base station transmits a first spread spectrum signal having a first code. For each received first signal, the subscriber unit transmits a second spread spectrum signal having a second code.
The second spread spectrum signal is time synchronized with its received first signal. An impulse response of each received first signal is analysed to determine a first received component. At each base station, an impulse response of that base station's received second signal is analyzed to determine a first received component. A distance between each base station and the subscriber unit is determined. The distance determination is based on in part a timing difference between the received signal and the transmitted signal and the determined first received component for the second signals. The location of the subscriber unit is based on in part the determined distances, a fixed location of 15 each base station and a maximum likelihood estimation.
Thus, according to one aspect, the present invention provides a method for geographically locating a subscriber unit using a plurality of base stations in a wireless CDMA communication system, each base station transmitting a first spread spectrum signal having a first code, for each received first signal, the 20 subscriber unit transmits a second spread spectrum signal having a second code Sto that received first signal's base station time synchronized with that received first signal, wherein for each received first signal at the subscriber unit, analysing an impulse response of multipath components of that received first signal to determine a first received component; at each base station, analysing an impulse response of multipath components of that base station's received second signal to determine a first received component; for each base station, determining a distance between that base station and the subscriber unit based on in part a timing difference between the second code of the received second signal and the first code of that base station's transmitted first signal and the determined first received component for that base station's received second signal; and determining the location of the subscriber unit based on in part the determined distances, a fixed location of each base station and a maximum likelihood estimation.
In an alternative aspect, the present invention provides a wireless CDMA communication system for locating a subscriber unit using a plurality of base stations, each base station transmitting a first spread spectrum signal having a first code, for each received first signal, the subscriber unit transmits a second spread spectrum signal having a second code to that received first signal's base station time synchronized with that received first signal, wherein the subscriber unit includes means for each received first signal, for analysing an impulse response to multiplath components of that received first signal to determine a first received component; each base station including means for analysing an impulse response of multipath components of that base station's received second signal to determine a first received component, means for determine a distance between that base station and the subscriber unit based on in part a timing difference between the second code of the received second signal and the first code of that base station's transmitted first signal and the determined first 15 received component for that base station's received second signal; and means for determining the location of the subscriber unit based on in part the determined distances, a fixed location of each base station and a maximum likelihood *estimation.
BRIEF DESCRIPTION OF THE DRAWINGS 20 Figure 1 is an illustration of a simplified, prior art CDMA system.
S•Figure 2 is an illustration of a prior art CDMA system.
Figure 3 is a block diagram of major components within a prior art CDMA system.
Figure 4 is a block diagram of components within a prior art CDMA system.
Figure 5 is an illustration of a global pilot signal and an assigned pilot signal being communicated between a base station and a subscriber unit.
WO 00/57661 PCT/US99/20257 Figure 6 is a block diagram of a first embodiment of the present invention using at least three base stations.
Figure 7 is an illustration of locating a subscriber unit using the first embodiment of the present invention with at least three base stations.
Figure 8 is a block diagram of a second embodiment of the present invention showing components used in a subscriber unit.
Figure 9 is an illustration of locating a subscriber unit using the second embodiment of the present invention with two base stations.
Figure 10 is an illustration of locating a subscriber unit using the second embodiment of the present invention with more than two base stations.
Figure 11 is a detailed illustration of the third embodiment of the present invention having a base station with multiple antennas.
Figure 12 is an illustration of the third embodiment having a base station with multiple antennas.
Figure 13 is a block diagram of components used in the third embodiment.
Figure 14 is an illustration of multipath.
Figure 15 is a graph of a typical impulse response of multipath components.
Figure 16 is a block diagram of components within a fourth embodiment correcting for multipath.
WO 00/57661 PCT/US99/20257 DESCRIPTION OF THE PREFERRED EMBODIMENTS The preferred embodiments will be described with reference to the drawing figures where like numerals represent like elements throughout.
Shown in Figure 1 is a simplified CDMA communication system. A data signal with a given bandwidth is mixed with a spreading code generated by a pseudo random chip code sequence generator producing a digital spread spectrum signal.
Upon reception, the data is reproduced after correlation with the same pseudo random chip code sequence used to transmit the data. Every other signal within the transmission bandwidth appears as noise to the signal being despread.
For timing synchronization with a receiver, an unmodulated pilot signal is required for every transmitter. The pilot signal allows respective receivers to synchronize with a given transmitter, allowing despreading of a traffic signal at the receiver.
In a typical CDMA system, base stations send global pilot signals to all subscriber units within their communicating range to synchronize transmissions in a forward direction. Additionally, in some CDMA systems, for example a B-
CDMA
T M system, each subscriber unit sends a unique assigned pilot signal to synchronize transmissions in a reverse direction.
Figure 2 illustrates a CDMA communication system 30. The communication system 30 comprises a plurality of base stations 361, 362 36n. Each base station WO 00/57661 PCT/US99/20257 361, 362 36n is in wireless communication with a plurality of subscriber units 401, 402 40n, which may be fixed or mobile. Each subscriber unit 401, 402 communicates with either the closest base station 361 or the base station 361 which provides the strongest communication signal. Each base station 361, 362 36, is in communication with other components within the communication system 30 as shown in Figure 3.
A local exchange 32 is at the center of the communications system 30 and communicates with a plurality of network interface units (NIUs) 34i, 34 34,.
Each NIU is in communication with a plurality of radio carrier stations (RCS) 381, 382 38n or base stations 361, 362 36n. Each (RCS) 381, 38 38, or base station 361, 362 36n communicates with a plurality of subscriber units 401, 402 within its communicating range.
Figure 4 depicts a block diagram of the pertinent parts of an existing spread spectrum CDMA communication system. Each independent base station 361, 36 36n generates a unique global pilot signal using a global pilot chip code generating means 421 and spread spectrum processing means 441. The global pilot chip code generating means 42, generates a unique pseudo random chip code sequence. The unique pseudo random chip code sequence is used to spread the resultant signals bandwidth such as to 15 MHZ as used in the B-CDMATM air interface. The spread spectrum processing means modulates the global pilot chip code sequence up to a WO 00/57661 PCT/US99/20257 desired center frequency. The global pilot signal is transmitted to all subscriber units by the base station's transmitter 461.
A receiver 48, at a subscriber unit 40, receives available signals from a plurality of base stations 36,, 362 36.. As shown in Figure 5, the global pilot travels from the base station 36, to the subscriber unit 40, and can be represented as: c Equation (1) The time the signal travels from the base station 36, to the subscriber unit 4 0
I,
equals the distance between the base station 36, and subscriber unit 401, divided by the speed of light, c.
Referring back to Figure 4, a global pilot chip code recovery means 541 within the subscriber unit 40, can receive global pilot chip code sequences from a plurality of base stations 361, 362 36.. The subscriber unit 401 generates a replica of a global pilot chip code sequence and synchronizes the generated replica's timing with the received global pilot 501. The subscriber unit 40, also has a processor 821 to perform the many analysis functions of the subscriber unit 401.
The subscriber unit 40, generates an assigned pilot signal 52, using assigned pilot chip code generating means 561 and spread spectrum processing means 58,.
The assigned pilot chip code generating means 561 generates a pseudo random chip code sequence with its timing synchronized with the recovered global pilot chip code WO 00/57661 PCT/US99/20257 sequence. As a result, the assigned pilot chip code sequence is delayed by with respect to the base station 361, 362 36,. The spread spectrum processing means 58, generates the assigned pilot signal 52, by modulating the assigned pilot chip code sequence up to a desired center frequency. The assigned pilot signal 521 is transmitted to all base stations 36,, 362 36. within range to receive the assigned pilot signal 52,.
The base station 36, receives the assigned pilot signal 52, with the base station's receiver 621. The received assigned pilot 52, travels the same distance d, as the global pilot signal 50, as shown in Figure 5. Accordingly, the received assigned pilot signal will be delayed by T 1 with respect to the mobile unit 40, and by 2T 1 with respect to the global pilot 50, generated at the base station 36,.
Since the chip code sequence of the assigned pilot 52, received at the base station 36, will be delayed by 2t, with respect to the chip code sequence of the global pilot signal 501 generated at the base station 36,, the round trip propagation delay, 2r 1 can be determined by comparing the timing of the two chip code sequences. Using the round trip propagation delay, 2T 1 the distance d, between the base station 36, and subscriber unit 40, can be determined by: c 2,.
2 Equation (2) WO 00/57661 PCT/US99/20257 If a spreading sequence having a chipping rate of at least 80ns is used and the communication system has the ability to track 1/16 t of a chip, the distance d. can be measured to within 2 meters.
Figure 6 is a block diagram of a first embodiment of the present invention.
No additional hardware is required in the subscriber unit 401. The only changes are implemented by software within the subscriber unit's processor 82, and the processors 661, 662... 66,, 68, 701, 70 70, located within the base station 361, NIU 341 or Local Exchange 321, Precincts 741, 74, 74, and Ambulance Dispatcher 76.
The subscriber unit 401 is sent a signal by a base station 361 indicating that a 911 call was initiated and to begin the subscriber location protocol. Upon receipt, the subscriber unit 40, will sequentially synchronize its transmission chip code sequence to at least three base stations' chip code sequences. To allow reception by the base stations 362, 363 36n outside of the subscriber unit's normal communicating range, these transmissions will be sent at a higher than normal power level temporarily over-riding any adaptive power control algorithms.
A processor 661 within each base station 361, 362 36, is coupled to the assigned pilot chip code recovery means 641 and the global pilot chip code generator 421. The processor 661 compares the two chip code sequences to determine the round trip propagation delay Tl, ,2 t, and the respective distance d 2 d n between the subscriber unit 401 and the respective base station 361, 362 36,.
WO 00/57661 PCT/US99/20257 Within either a NIU 34, or the local exchange 32, a processor 68 receives the distances d 1 d 2 d, from the processors 661, 662 66, within all the base stations 361, 362 36,. The processor 68 uses the distances d 2 d, to determine the location of the subscriber unit 401 as follows.
By using the known longitude and latitude from three base stations 361, 362, 363 and distances dl, d 2 d 3 the location of the subscriber unit 40, is determined. As shown in Figure 7 by using the three distances d 2 d 3 three circles 781, 782, 783 with radiae 801, 802,803 are constructed. Each circle 781, 78, 783 is centered around a respective base station 361, 362,363. The intersection of the three circles 781, 782, 783 is at the location of the subscriber unit Using the Cartesian coordinates, the longitude and latitude corresponding with each base station 361, 362 36, is represented as where X, is the longitude and Yn is the latitude. If X, Y represents the location of the subscriber unit 401, using the distance formula the following equations result:
(X
1
-X)
2 2 dZ Equation (3)
(X
2
-X)
2
+(Y
2
-Y)
2 d 2 Equation (4)
(X
3
-X)
2 +(y 3
-Y)
2 d3 Equation In practice due to small errors in calculating the distances di, dz dz, Equations 3, 4 and 5 cannot be solved using conventional algebra. To compensate for the errors, a maximum likelihood estimation is used to determine the location and WO 00/57661 PCT/US99/20257 are well known to those skilled in the art. For increased accuracy, additional base stations 364, 365 36, can be used to calculate additional distances for inclusion in the estimation analysis.
The subscriber unit's location is sent through the communication system to at least one precinct 74,, 742... 74, and an ambulance dispatcher 76. A processor within each precinct 741, 742... 74, and the ambulance dispatcher 76 receives the location of all 911 calls originating in the system and displays the location on a conventional computer monitor 721. The display comprises a listing of all 911 calls and addresses on a geographic map.
.0 An alternate approach reduces the number of processors by transmitting raw data through the communication system 30 and processing the raw data at a single site.
Figure 8 is a second embodiment of a location system. At least two base stations 361, 362 36, have their internal timing synchronized with each other and transmit their respective global pilot signals 521, 522 52. with time synchronized chip code sequences. The subscriber unit 40, receives the global pilots 521, 522 52,. However, the received global pilots 52,, 522 52. are not synchronized. The global pilot 52, from a first base station 36, will travel distance d, and is delayed by
T
1 The global pilot 522 from a second base station 362 travels distance d 2 and is 0 delayed by -r 2 The subscriber unit 40, recovers each base station's global pilot chip -11- WO 00/57661 PCT/US99/20257 code sequence with its global pilot chip code recovery means 541. A processor 82, within the subscriber unit 401 is coupled to each global pilot chip code recovery means 541, 52, 54,. The processor 82, compares the chip code sequences of each pair of pilot chip code sequences and calculates the time differences At,, At 2 Atn between the sequences as follows.
Within the subscriber unit 401, the chip code sequences used by each base station 361, 362 36, are stored. After synchronizing with.the first base station's pilot 361, the processor 821 will store where within the sequence synchronization was obtained. This process is repeated for the other base stations 362, 363 36,. The 0 synchronization process can be done sequentially (synchronizing to the first base station's chip code sequence then the second, etc.) or in parallel (synchronizing to all base stations at the same time).
By using the relative time difference between Tz, T 2 each base station's chip code sequence and knowing that each base station's pilot was sent at the same time, with two base stations the time differences are calculated as follows: :At 2
-T
1 Equation (6) At 2 3-T2 Equation (7) The time differences At 1 At 2 At, are transmitted to at least one of the base stations 361.
-12- WO 00/57661 PCT/US99/20257 At least one base station 361 recovers the time difference data from the received signals using time difference recovery means 841. The time difference data is sent with the distance data d, through the communications system to a processor 68. The processor 68 determines the location of the subscriber unit 401 using the time difference data At 1 At 2 At, and the distance data d 2 d, as follows.
Using information from only two base stations 361, 362 as shown in Figure 9, the processor uses distances d 1 d 2 to create two circles 781, 782. Using the time difference, At 1 a hyperbola 861 can be constructed as follows.
All the points along the hyperbola 861 receive the global pilot signals 521, 522 0 from the synchronized base stations 361, 362 with the same time difference, At 1 The time difference At, can be converted to a distance difference Ad 1 by substituting At, for t, and Ad 1 for d, in Equation 1. Using the distance formula and X, Y as the location of the subscriber unit 401, the following equation results: Ad, (X 1 2
_-X
2 2 2+( 2 Equation (8) By using Equation 8 with Equations 3 and 4 in a maximum likelihood estimation, the location of the subscriber unit 401 can be determined. The subscriber unit's location is subsequently sent to the nearest police precinct 741, 742 74, and 0 ambulance dispatcher 76 in the cellular area.
WO 00/57661 PCT/US99/20257 For improved accuracy, additional base stations 361, 362 36, are used.
Figure 10 shows the invention used with three base stations 361, 362, 363. The distances d 1 d 2 d 3 are used to create three circles 781, 782, 783. Using time differences At 1 At 2 two intersecting hyperbolas 861, 86, are constructed. With maximum likelihood estimation, the subscriber units' location calculated with two hyperbolas 861, 862, and three circles 781, 782, 783 yields greater accuracy.
As shown in Figure 8, the subscriber unit 401 is required to process each global pilot chip code sequence to determine the time differences At 1 At At..
An alternate approach removes the processing from the subscriber unit 401.
With reference to Figure 6, the mobile unit 401 will synchronize the assigned pilot to one of the base station's global pilot chip code sequences, such as the nearest base station 361 with a delay of 1r. The assigned pilot 501 is transmitted to all base stations 361, 362 36,. The assigned pilot 501 will be received at each base station with a respective delay, t 1
T
1 Ti T2, T 1 3 Each base station 361, 362 36, will send the delayed chip code sequence along with the calculated distance to a processor 68 located in a NIU 341 or local exchange 32. The processor 68 will calculate the time differences At 1 At2 At, by comparing the received assigned pilot chip code sequences. Since all received assigned pilot chip code sequences are delayed by T, the 1 delay will cancel out of the resultant time differences At 1 At2 WO 00/57661 PCT/US99/20257 At,. Accordingly, the subscriber unit 40, can be located using hyperbolas 861, 862 as previously described.
Another embodiment shown in Figures 11, 12 and 13 uses a base station 36, with multiple antennas 881, 882... 88,. Two of the antennas 881, 882 lie along a centerline 92 at a known distance, 1, apart as shown in Figure 11. Both antennas 881, 882 receive the assigned pilot signal 901, 902 from the subscriber unit 401.
However, the antenna 882 further away from the subscriber unit 40, receives the signal over a slightly longer distance d 1 and with a slight delay with respect to the nearer antenna 881. This delay results in a carrier phase difference, between the 0 signals received at each antenna as shown on Figure 13. A processor 66 using the received carrier phase difference and the chip code sequence recovered by each assigned pilot chip code recovery means 96,, 962 96, can determine the location of the subscriber unit 40, as follows.
As shown in Figure 12, the subscriber unit 40, is located at distance d, at angle a from the centerline 92 of the antennas 881, 882. As seen at the scale of Figure 12 both received assigned pilot signals 901, 902 appear to be coincident.
However, as shown in Figure 11, the received assigned pilot signals 90,, 902 are slightly separated. The received assigned pilot signal 90, returning to the first antenna 88, travels a distance The received assigned pilot signal 902 returning WO 00/57661 PCT/US99/20257 to the second antenna 882 travels a slightly longer distance As shown in Figure 11, the difference between the two distances d 1 is a distance m.
Since the distances d 1 between the antennas 881, 882 and the subscriber unit 401 are much larger than the distance I between the antennae 881, 882 both received assigned pilot signals 901, 902 follow approximately parallel paths. By constructing a right triangle using a point 94 which is distance d, from the subscriber unit 401 as shown in Figure 11, the angle can be determined by the following geometric relationship: *c COS 1 Equation (9) The distance m can be determined by using the carrier phase difference, between the two received signals 90,, 902 as follows: m~ Equation 27r The distance m equals the phase difference between the two signals, 4, in radians multiplied by the wavelength of the signal, 1, divided by 27. The wavelength, 1, can be derived from the known frequency f of the assigned pilot signal as follows: c/f.
Equation (11) -16- WO 00/57661 PCT/US99/0257 The processor 68 also compares the chip code sequences of the global pilot generating means 421 with the recovered assigned pilot chip code sequence to determine the distance d 1 as shown in Figure 6. Using both the angle and distance the processor 661 locates the subscriber unit 401 using simple geometry. There are many techniques well known to those skilled in the art to eliminate the ambiguity between locations above and below the antennas 881, 882. One such technique is using antennas employing sectorization. Subsequently, the subscriber unit's location is sent to the precincts 741, 742 74, and ambulance dispatcher 76. Additional antennas may be used to improve on the accuracy of the system.
0 An alternate embodiment uses more than one base station 36,, 362... 36,. A processor 68 located within either a NIU 34 or the local exchange 32 collects distance and angle information from more than one base station 36,, 362 36, as well as the time differences At,, At 2 At., between the base stations 361, 362... 36n.
Using the maximum likelihood estimation technique, the processor 68 determines a more accurate location of the subscriber unit 401.
A fourth embodiment corrects for multipath. Figure 14 illustrates multipath.
A signal such as a global pilot signal is transmitted from a base station 361. The signal follows a multitude of paths 981, 982 98. between the base station 361 and subscriber unit 401.
-17fl&/lOafli 09:49 FAX 215 568 6499 VOLPE AND KoENIG,P..U 0905 ,19-04-2001 US 009225 Figure 13 is a graph showing the impulse response 136 of the received inultipath components. Since each received multipath component travels a unique path, it arrives at a receiver with a propagation delay determined by the length of the path 981, 982- 98,. The impulse response 106 shows the collective signal magnitude of all the inultipath components received at each propagation del ay.
The previously described subscriber unit location techniquos assumed the subscriber unit 40, synchronizes with the line of sight maultipath component 98, traveling distance However, if the subscriber unit synchronizes with a nonline of sight multipath component 991, 982.. 98,, the distance calculation will be in error due to the delay MD, as shown in Figure Figure 16 is a system correcting for errors resulting from mnultipath. The global pilot 50, is. sent from the base station 36, to subscriber unit 401 The subscriber unit 40 collects all of the multipath components using a multipath receiver 102, such as disciosedin U.S. Patent Application No.. 081669,7.69, Lomp et al. A processor 82, within the subscriber unit 40, analyzes the impulse response 100 of the received global pilot signal 501.
Since the line of sight multipath component 98, travels the shortest distance di, the first received component 98, is the line of sight component. if the line of sight component is not received, the first received component 98, will be the closest and, accordingly, the best available estimte for the line of sight component. The Wpangszeit 19.APr. 15:48 AMENDED SHEET WO 00/57661 PCT/US99/20257 processor 821 compares the chip code sequence of the first received component 981 with the chip code sequence used to synchronize the assigned pilot chip code sequence. This comparison determines the delay due to multipath, MD,. The multipath delay, MD 1 is transmitted to the base station 361.
A processor 661 and multipath receiver 1041 within the base station 361 perform the same analysis on the received assigned pilot signal. As a result, the multipath delay, MD 2 of the assigned pilot signal is determined. Additionally, multipath delay recovery means 1061 recovers the transmitted global pilot signal's multipath delay MDI for use by the processor 661. The processor 66, compares the generated global pilot chip code sequence to the recovered assigned pilot chip code sequence to determine the round trip propagation delay 212. To correct for multipath, the processor 661 subtracts both the global pilot signal's multipath delay MDi and the assigned pilot signals multipath delay MD, from the calculated round trip propagation delay, 2t 1 The corrected round trip propagation delay is used to determine the subscriber unit's location in one of the techniques as previously described.
Although the invention has been described in part by making detailed reference to certain specific embodiments, such detail is intended to be instructive rather than restrictive. It will be appreciated by those skilled in the art that many WO 00/57661 PCT/US99/20257 variations may be made in the structure and mode of operation without departing from the scope of the invention as disclosed in the teachings herein.
Claims (12)
1. A method for geographically locating a subscriber unit using a plurality of base stations in a wireless CDMA communication system, each base station transmitting a first spread spectrum signal having a first code, for each received first signal, the subscriber unit transmits a second spread spectrum signal having a second code to that received first signal's base station time synchronized with that received first signal, wherein for each received first signal at the subscriber unit, analysing an impulse response of multipath components of that received first signal to determine a first received component; at each base station, analysing an impulse response of multipath components of that base station's received second signal to determine a first received component; for each base station, determining a distance between that base station and the subscriber unit based on in part a timing difference between the second code of the received second signal and the first code of that base station's transmitted first signaland the determined first received component for that base o station's received second signal; and determining the location of the subscriber unit based on in part the determined distances, a fixed location of each base station and a maximum likelihood estimation.
2. The method of claim 1 wherein the base stations are time synchronized to each other; the subscriber unit determines a time difference of reception between the received first signals and transmits a representation of the time difference; and the maximum likelihood estimation uses the determined time difference to determine the subscriber unit location.
3. The method of claim 1 wherein the base stations are timed synchronized to each other; a time difference of reception between each base station's received second signal is determined; and the maximum likelihood estimation uses the determined time difference to determine the subscriber unit location.
4. The method of claim 2 or 3 including using a formula for a hyperbola associated with each time difference and a formula for a circle associated with each determined distance in the maximum likelihood estimation.
The method of any one of the preceding claims, wherein the transmission of each second signal is time synchronized to the determined first received component of its received first signal.
6. The method of any one of claims 1 to 4, including the subscriber unit transmitting, for each base station, a representation of a time difference between the first received component and a synchronization time of the transmitted second signal of that base station. oo
7. A wireless CDMA communication system for locating a subscriber unit using a plurality of base stations, each base station transmitting a first spread spectrum signal having a first code, for each received first signal, the subscriber •."unit transmits a second spread spectrum signal having a second code to that o received first signal's base station time synchronized with that received first signal, wherein the subscriber unit includes means for each received first signal, for analysing an impulse response to multiplath components of that received first lli. signal to determine a first received component; each base station including means for analysing an impulse response of multipath components of that base station's received second signal to determine a first received component, means for determine a distance between that base station and the subscriber unit based on in part a timing difference between the second code of the received second signal and the first code of that base station's transmitted first signal and the determined first received component for that base station's received second signal; and means for determining the location of the subscriber unit based on in part the determined distances, a fixed location of each base station and a maximum /likelihood estimation.
8. The system of claim 7 wherein the base stations are time synchronized to each other; the subscriber unit having means for determining a time difference of reception between the received first signals; and means for transmitting a representation of the time difference; and the maximum likelihood estimation using the determined time difference to determine the subscriber unit location.
9. The system of claim 7 wherein the base stations are time synchronized to each other; the system further including means for determining a time difference of reception between each base station's received second signal; and the maximum likelihood estimation using the determined time difference to determine oe° e othe subscriber unit location.
10. The system of claim 8 or 9 including using a formula for a hyperbola associated with each time difference and a formula for a circle associated with each determined distance in the maximum likelihood estimation. .i
11. The system of any one of claims 7 to 10 wherein the transmission of each second signal is time synchronized to the determined first received component of its received first signal.
12. The system of any one of claims 7 to 10 wherein the subscriber unit includes means for transmitting for each base station, a representation of a time difference between the closest line of sight component and a synchronization time of the transmitted second signal of that base station. DATED this 12 th day of November 2002 INTERDIGITAL TECHNOLOGY CORP WATERMARK PATENT TRADEMARK ATTORNEYS 2 1 ST FLOOR, "ALLENDALE SQUARE" 77 ST GEORGE'S TERRACE PERTH WA 6001
Priority Applications (1)
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|---|---|---|---|
| AU2002302027A AU2002302027B2 (en) | 1999-03-22 | 2002-11-15 | Method and system for locating a mobile subscriber in a cdma communication system |
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| US09/274,081 US6603800B1 (en) | 1999-03-22 | 1999-03-22 | CDMA location |
| US09/274081 | 1999-03-22 | ||
| PCT/US1999/020257 WO2000057661A1 (en) | 1999-03-22 | 1999-09-03 | Method and system for locating a mobile subscriber in a cdma communication system |
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- 1999-09-03 CA CA2489816A patent/CA2489816C/en not_active Expired - Fee Related
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